Re: [PATCH] Percpu tag allocator

From: Kent Overstreet
Date: Thu Jun 13 2013 - 17:57:52 EST

On Thu, Jun 13, 2013 at 02:50:09PM -0700, Tejun Heo wrote:
> (cc'ing Rafael and Oleg)
> On Thu, Jun 13, 2013 at 02:14:25PM -0700, Kent Overstreet wrote:
> > Yeah, I think you're definitely right. (I only started reading up on the
> > freezer stuff yesterday, though).
> >
> > Do you know offhand what existing (i.e. slab) allocators do? Whatever
> > they do should make sense for us.
> I don't think the memory allocator does anything. Memory allocations
> are guaranteed to make forward progress and everything should still be
> working while freezing, so it doesn't need to do anything special. If
> the tag allocator is to be used only by kernel proper - say drivers,
> block layer, it shouldn't need to do anything special. If it's
> directly exposed to userland via something like aio and the userland
> is involved in guaranteeing forward progress - ie. freeing of tags -
> then the allocator would need to be able to fail, I think.

That's a good point - as long as whatever is allocated is guaranteed to
be freed in bounded time, we should be fine.
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